In recent years, fine particles in nanometer order are considered to be applied to various devices. For example, metal fine particles of nickel are used for a ceramic capacitor at present, and fine particles with a particle diameter of 200 nanometers or less having good dispersibility are considered to be used for a next generation ceramic capacitor.
Furthermore, fine particles of silicon monoxide (SiOx: x=1 to 1.6) having a lower oxygen content than silicon dioxide are utilized as an antireflection film of an optical lens or a deposition material of a gas-barrier film for food packaging. Recently, application of the fine particles to an anode material of a lithium-ion secondary battery is expected.
Some common methods of producing fine particles in nanometer order include, a method of introducing a bulk material as a raw material together with beads such as ceramic beads and zirconia beads, and miniaturizing the material into particles, a method of melting and evaporating a material and spraying the material to air or water to obtain fine particles and a method of chemically obtaining fine particles by electrolysis or reduction and so on. Among them, a method of producing fine particles in a vapor by using thermal plasm (approximately 10000° C.) such as high-frequency plasma or arc plasma is considered extremely useful because the produced fine particles are excellent in dispersibility with less contamination and composite fine particles formed of plural kinds of materials can be easily composed (for example, refer to Japanese Patent No. 5318463 (Patent Document 1)).
FIG. 4 shows a schematic cross-sectional view of a production apparatus of fine particles using thermal plasma according to a related-art example 1.
A plasma generator 202 (high-frequency plasma torch) is provided at a ceiling part of a fine particle generating chamber 201, which is connected to a fine particle collection device 204 through piping 203. Thermal plasma is generated in the plasma generator 202. A material is introduced into the thermal plasma to form fine particles in the fine particle generating chamber 201. After the fine particles are cooled by a cooling gas supplied from a gas supply port 205 in the fine particle generating chamber 201, the fine particles are fed to a cyclone 206 through the piping 203. In the cyclone 206, unevaporated materials or rough particles other than fine particles are separated, and fine particles are fed to the fine particle collection device 204 through the piping 203. The fine particles are collected in the fine particle collection device 204. The fine particle collection device 204 is connected to a surge tank 207 and a circulation pump 208 through the piping 203 and is further connected to the gas supply port 205 through the piping 203, which makes a structure of circulating the gas. An automatic pressure regulating valve 209 and a gas header 210 are provided between the circulation pump 208 and the gas supply port 205 to thereby make variation in the cooling gas quantity stable. A thermal exchanger 211 is installed on an entrance side of the circulation pump 208 to suppress temperature increase of the gas and cool generated fine particles.